This invention relates to a rolling bearing apparatus, such as a tapered roller bearing and an angular contact ball bearing, used under a preload.
A tapered roller bearing and an angular contact ball bearing are used while subjected to an axial preload. For example, in a gear-type drive transmission unit of an automobile such as a transmission unit, a tapered roller bearing is provided at a required portion thereof (for example, at a final reduction gear portion in the transmission unit). As shown in FIG. 5A, in this tapered roller bearing 111, a rotation shaft 115 is press-fitted in an inner ring 133, and an outer ring 132 is fitted to a housing 125 of a transmission case, and thereafter a preload is applied toward one side (indicated by arrow a) in an axial direction. When the preload is thus applied, the outer ring 132 receives component forces on inclined rolling contact surfaces of tapered rollers 134, and is displaced axially and radially, and a left end surface 132c and an outer peripheral surface 132b of the outer ring 132 are pressed respectively against an inner end surface 125c and an inner peripheral surface 125a of the housing 125, thereby supporting the preload.
On the other hand, as one part of recent attempts to achieve a lightweight design, a transmission case (housing) has been formed of light metal such as an aluminum (Al) alloy. Among structural materials, Al is the highest in linear expansion coefficient (about 23.5×10−6/° C. at room temperature: The unit of the linear expansion coefficient will hereinafter be expressed by ppm/° C.), and its linear expansion coefficient is quite different from a linear expansion coefficient (about 12 ppm/° C. at room temperature) of steel (Fe-based material) forming the rotation shaft and the tapered roller bearing.
When the rotation shaft and the housing are made of the same material, a preload acting on the tapered roller bearing will not change considerably, since the rotation shaft and the housing are subjected to the same dimensional change due to a temperature change. However, when the housing is made of light metal, the amount of dimensional change of the housing due to a temperature rise is larger than that of the rotation shaft, which leads to a fear that the preload may be eliminated.
More specifically, as shown in FIG. 5B, when the temperature of the transmission rises, the housing 125 and the rotation shaft 115 expand, and because of the difference in the amount of dimensional change due to this expansion, an inner periphery raceway surface 132a of the outer ring 132 is separated from the rolling contact surfaces of the tapered rollers 134 in a direction of arrow b. Namely, an axial clearance and a radial clearance of the tapered roller bearing change considerably because of the temperature change, so that the preload becomes insufficient. This insufficient preload invites the shaking of the gear, and causes the generation of noises.
In order to solve the above problem, JP-A-2006-153090 discloses a rolling bearing apparatus in which a preload is applied to an outer ring by a hydraulic pressure and a spring. More specifically, a cylinder of a tubular shape with a closed bottom is formed at a housing, and an outer ring is fitted in this cylinder so as to slide in an axial direction, and within this cylinder, a disk-shaped preload member (piston) is held against an axially-outer end of the outer ring to close an opening in this axially-outer end. A hydraulic fluid is supplied to a pressure chamber, surrounded by an inner surface of the cylinder and the preload member, by a hydraulic pump. Further, a compression coil spring is provided within the pressure chamber, and urges the preload member inward in the axial direction.
In this construction, a preload is applied to the preload member by a hydraulic pressure and the compression coil spring, and when the housing is changed in dimension in a larger amount than a rotation shaft and the outer ring because of a temperature rise, the outer ring is moved inward in the axial direction via the preload member under the influence of the compression coil spring and the hydraulic pressure, thereby suppressing the changing of an axial clearance and a radial clearance in the tapered roller bearing, thus overcoming a lack of the preload.
In the technique of JP-A-2006-153090, however, the hydraulic fluid need to be always supplied from a hydraulic pump to the pressure chamber in order to keep the hydraulic pressure within the pressure chamber at a constant level, and therefore there has been encountered a problem that energy consumption is high. Particularly when a mechanism for overcoming the above-mentioned lack of the preload is used in an automatic transmission, it may be proposed to supply part of a hydraulic fluid, used for the hydraulic control of this transmission, to the pressure chamber. In this case, however, it is necessary to increase a discharge of the hydraulic pump by an amount corresponding to the amount of the hydraulic fluid to be supplied to the pressure chamber, and this has invited a problem that additional energy is required.
In the technique of JP-A-2006-153090, the cylinder is formed into a large size (that is, a large diameter) so as to correspond to the overall size of the bearing. Therefore, the amount of dimensional change of the cylinder due to thermal expansion becomes large, so that a clearance between the cylinder and the preload member becomes large. On the other hand, only one O-ring is interposed between the outer peripheral surface of the preload member and the inner peripheral surface of the cylinder. Therefore, when the cylinder is increased in diameter by thermal expansion, the preload member is liable to be inclined, and oil is liable to leak through a clearance between the bearing and the housing, thus inviting a possibility that the sufficient preload can not be applied.
Furthermore, in order to prevent the pressure within the pressure chamber from increasing when the housing is cooled from the temperature-elevated condition, the O-ring interposed between the outer peripheral surface of the preload member and the inner peripheral surface of the cylinder allows the oil to pass therebetween, and therefore this O-ring can not completely prevent the leakage of the oil.